The invention relates to a vehicle impact detection sensor system, in particular for providing an input variable for an activation logic unit or for generating an activation signal for an active occupant protection system.
Active restraint systems such as, for example, airbags or seat belt pretensioning devices frequently comprise a vehicle impact detection sensor system in which there are provided acceleration sensors which respond to an impact-relevant acceleration which occurs in the case of an impact accident situation. Although active restraint systems which are based on the pyrotechnic principle are capable of reacting quickly, there are accident situations such as, for example, side collisions directly into the door region of a motor vehicle in the case of which the impact is not detected by acceleration sensors positioned conventionally until relatively late.
A vehicle impact detection sensor system of the type mentioned at the beginning is disclosed in DE 195 46 715 A1. In this reference, an airbag sensor system is described which comprises a plurality of microwave sensors which in each case have a transmitting and receiving stage. These microwave sensors are arranged next to one another in a door of the body such that they monitor the adjacent external vehicle surroundings. For this purpose, they generate a frequency signal in the region of, for example, 76 GHz and scan a distance range of approximately 1 m for possible objects which are moving towards the vehicle, doing so by detecting a possibly reflected frequency signal and evaluating the latter using the Doppler frequency technique. The Doppler frequency can be used to determine the speed at which a collision object is moving towards the microwave sensors, whereupon the airbag is activated when a threshold value is exceeded.
DE 92 15 383 U1 discloses an optical crash sensor which is arranged in a door of the body and is suitable, in particular, for detecting side impact accidents in good time. This sensor comprises a light-guiding path with lenses and stops for focusing a light beam which is directed onto a phototransistor. In the case of a side impact, the light-guiding path is deformed, and this causes a change in a signal of the phototransistor, and permits a corresponding activation of active occupant protection systems. A similar side impact detection device with a light-guiding path, for example in a vehicle door, is described in the Laid-Open Patent Application DE 195 37 383 A1.
DE 43 22 488 A1 describes arranging piezoelectrically resistive pressure sensors on the door inner panel of a door in the body of a motor vehicle, which in the event of a side impact detect a sudden rise in pressure of the ambient air and thereupon activate an active occupant protection system.
The Laid-Open Patent Application DE 43 00 653 A1 describes a collision sensor which includes a device generating a magnetic field and an electric conductor which changes its position relative to the magnetic field in the event of a deformation in a vehicle part at risk of collision. The amplitude, representative of the deformation rate, of the electric voltage induced in the electric conductor by the change in position is detected and suitably evaluated.
The Laid Open Patent Application DE 42 42 230 A1 discloses a side impact detection sensor system which has an electric capacitor which forms a frequency-determining circuit element of an oscillator circuit which is connected to a frequency/voltage transformer for outputting an impact-indicative electric voltage.
A further known technique for side impact detection is to insert a strain gauge in the door region of a motor vehicle, or to position acceleration sensors on the door outer panel.
It is the object of the invention to create a vehicle impact detection sensor system of the type mentioned at the beginning which is also particularly suitable for activating an active occupant protection system protecting against side impact, and permits early activation in the process.
This object is achieved by means of a vehicle impact detection sensor system where the impact-relevant reflexion surface is characteristically a surface permanently connected to the vehicle, in particular an outer surface of the vehicle. It is possible with the aid of this sensor system quickly to detect a threatening accident situation as early as on the basis of a slight movement of the impact-relevant reflexion surface relative to the sensor-carrying vehicle superstructure, and to make use of this, for example, for the purpose of early activation of an active occupant protection system.
In a development of the invention, a detector is provided for detecting an oscillatory movement of the impact-relevant reflexion surface. It is possible in this way to avoid erroneous activation of active occupant protection systems on the basis of vibrations of the relevant vehicle outer surface.
In a development of the invention, a radar sensor is arranged in such a way that it emits radar waves into a cavity whose boundaries are formed at least partly by the impact-relevant reflexion surface. The radar receiver is arranged fittingly for this purpose such that it receives reflected radar waves from the cavity. This cavity can, for example, be one such as in the vehicle door. In this case, an incipient pressing inwards of the door outer skin causes a change in the cavity configuration for the radar waves reflected in it, and thus a corresponding Doppler frequency signal at the radar receiver. The filling of the cavity with reflected radar radiation can be used to monitor a particularly large impact-sensitive surface area.